Pneumatic control system for radar antenna



pt. 13, 1 T. c. KIRSTEIN 3,

PNEUMATIC CONTROL SYSTEM FOR RADAR ANTENNA Filed Feb. 21, 1964 2 Sheets-Sheet l FIG. 3 INVENTOR.

THOMAS C. KIRSTEIN J 1* ATTORNEY p 13, 1966 T. c. KIRSTEIN 3,273,157

PNEUMATIC CONTROL SYSTEM FOR RADAR ANTENNA Filed Feb. 21, 1964 2 Sheets-Sheet 2 ALTITUDE IN THOUSAND FEET INVENTOR. THOMAS C. KIRSTEIN BYISLLW ATTORNEY United States Patent 3,273,157 PNEUMATIC CONTROL SYSTEM FOR RADAR ANTENNA Thomas C. Kirstein, Anaheim, Calif., assignor to North American Aviation, Inc. Filed Feb. 21, 1964, Ser. No. 346,569 2 Claims. (Cl. 343-781) This invention relates to a system for controlling a flexible reflector of a radar antenna and more particularly to a pneumatic control system for causing the flexible reflector of a radar antenna to provide a selected one of two alternative and distinct radar beam patterns.

Certain dual pattern antenna actuation systems introduce a gas at the rear or in front of a reflector diaphragm for urging it frontwards or backwards within a chamber shell thereby changing a radar antenna beam pattern from sharp to broad depending on reflector position. Use of gas introduction or positive pressure actuation systems may result in a Bourdon tube eifect or ballooning, well recognized in the art, which tends to distort the resultant antenna pattern.

Such actuation systems are usually comprised of rotating vane-type pumps. As the vane portion rotates, a certain incremental volume of pressurized gas is emitted into an antenna chamber shell to urge a reflective diaphragm in one direction. Transfer time for the diaphragm is limited, therefore, by the size and speed of the rotor system. If system size increases to emit a greater volume of gas into the chamber, weight is also increased, although the size of a given antenna system limits the size of a positive actuation system which can be used therewith. F or example, the ports to the antenna chamber may limit the quantity of gas delivered by the rotating vanes.

Increases in rotor speed may also improve transfer time by delivering gas into the chamber faster, but such increases are often accompanied by increased motor size or more complex and more unreliable motors. The additional size and weight 'as well as decreased reliability may prohibit use of a positive pressure actuated system in high speed aircrafts Where weight and size are important considerations.

The lubricated parts of the pressurized gas type system often introduce contaminants such as lubrication oil into a radar chamber shell housing the diaphragm. Further, bearings used with the rotor may become contaminated by materials resulting from wear during operation, resulting in pump failure or decreased reliability.

A system is required whereby ballooning (and, therefore, antenna pattern distortion) is substantially eliminated. In addition, such systems should require no moving parts, be small and light weight, as well as having a relatively fast diaphragm transfer time. For example, if a system is used in a high speed aircraft, the transfer time must be small, otherwise before the pattern can be changed, errors might be experienced in interpreting the radar data provided by the antenna. However, prior art systems weighing, for example, four pounds, require as long as 35 seconds to effect a change in the diaphragm position when used with a chamber shell having a volume of approximately 8800 cc. Such a system typically has a life of approximately 200 hours of operation. Such long response time and short useful life limit the applicability of such a system in high-speed aircraft.

The inventive system, to be described hereinafter, satisfies the above requirements and overcomes the defects of the art, in that there are no moving parts. Hence, improved reliability results and a source of contaminants is also removed. The system is also light weight and small. For example, a typical design, comparable in volumetric capacity with the above four pound exemplary prior art positive pressure system, may weigh less than 'of air with a vane-pump system is avoided.

ICC

one pound and demonstrate a useful life as high as 1000 hours. Further, by means of the invention, the responsive time is significantly decreased. For example, for the exemplary systems, the response time may be reduced from 35 seconds to approximately 3 seconds, depending on altitude. Such speed of response is increased because the inherent limitation upon the incremental volume Morever, the improved response does not result in the detrimental ballooning effect associated with a positive pressure type actuation system.

It is an object of this invention to achieve two alternative radar patterns by means of a pneumatic control system.

It is another object of this invention to improve switching time from one reflector position to another over that provided by vane-type pump pressurized systems.

Another object of this invention is to eliminate the Bourdon tube effect of systems using pressurized gas for shifting reflector positions.

These and other objects of the invention will become apparent from the description contained herein.

The invention is comprised of ejector mean-s such as a jet pump which provides 'a vacuum source for holding a flexible diaphragm of an antenna in a selected one place or of two alternative positions, regulator means disposed between the ejector means and the fluid source of the ejector means for regulating the pressure of the fluid to the ejector, valve means such as a four-Way, two-position solenoid valve for selecting a desired diaphragm position. Safety means such as a relief valve may be added to prevent rupture of the diaphragm under certain conditions.

FIG. 1 is a schematic arrangement in partial section of a pneumatic system with the selector valve in one position.

FIG. 2 is a graph representation of reflector transfer time versus altitude at various regulated pressures for the pneumatic system.

FIG. 3 is a cross sectional view of the ejector.

Referring now to FIG. 1, wherein a preferred embodiment of the invention is shown, a fluid such as 'air from an operating aircraft turbine engine, is conducted through tubing 10 to a primary or input port 26 of an ejector 1, for actuating ejector 1. Ejector 1 for the embodiment shown is a jet pump. For the pneumatic system described herein, the fluid use-d to actuate ejector 1 is bleed air from an aircraft turbine engine having a pressure of from 45 to 300 p.s.i.a. Ejector 1 is comprised of a mixing chamber 17 enclosing an exhaust port 16 (which exhausts to the atmosphere) and primary port 26 (having a tapered tube section 15 for exhausting fluid into port 16). Ejector '1 also includes secondary port 21 into which one end of tubing 13 connects, for example, by threaded mating.

Selector means 3, such as a four-way, two-position solenoid valve, is incorporated into the pneumatic system between a radar antenna 4 and the second end of tube 13 for selecting the desired diaphragm position of antenna 4.

Antenna 4, in one embodiment, may be comprised of a hollow plastic shell 5 containing a flexible deformable, metal-impregnated plastic diaphragm 6 as the reflector surface. For the embodiment described herein, the volume of the antenna is assumed to be 8800 cubic centimeters. Diaphragm 6 may be selectively urged to press against surface 7 or surface 8, depending on the position of selector means 6. For the embodiment shown in FIG. 1, the diaphragm is urged against surface 7 by the combined action of the selector position and ejector 1. Since the orientation of antenna 4 is mechanically oscillated during normal scanning operation thereof, fluid lines 11 and 12 connecting the antenna to the selector,

are made flexible. Flexible rubber hoses are suflicient for that purpose.

Safety means 9 such as a suction relief valve with filter are not necessary for a complete embodiment of the invention but may be added to prevent excessive vacuum from developing in the system. For example, valve means '9 may be set to open when the vacuum in tube or line 13 reaches approximately 6 inches of mercury, relative to the atmosphere. When the valve is open, the air flows from the atmosphere through means '9 and out ejector 1, thereby preventing rupture of the diaphragm.

In the normal operation of ejector 1, the exhaustion of pressurized gas from orifice 15 flows through chamber 17 to the exit of exhaust port 16 causing a reduction of pressure in chamber 17 in the vicinity of port 21, whereby fluid is exhausted from line 13 via exhaust port 16, in a manner under-stood in the art. Where, however, the inlet pressure at port 26 of ejector 1 exceeds a limit value, then choking occurs, whereby ejector 1 fail-s to effectively lower the pressure at port 21 and in line 13. In other words, the exhaust port 16 presents a restrictive orifice to volumetric flow rates in excess of a flow rate limit determined by a specific design configuration, whereby the load pressure in mixing chamber 17 at the vicinity of port 21 tends to increase rather than decrease. Such choking effect in mixing chamber 17 reduces, or may even prevent, operation of ejector 1 as intended.

To avoid such choking action, regulator 2 is interposed at the actuation input (port 26) of ejector 1 by means of tubing 28 for controlling the ejector primary air pressure, P at different altitudes and engine speeds. In the intended application of the embodiment of FIG. 1, the altitude is assumed to vary from to 75,000 feet. The ranges for the parameters stated herein are not intended to be exact, but are stated merely to give an indication of an operable range for a preferred embodiment of the pneumatic system. If regulator 1 is omitted, .then air from the turbine may cause a choking effect in the ejector at higher altitudes. For example, for a particular size and configuration of ejector 1, the air flow through mixing chamber 17 is restricted to a maximum volume value V If the flow of air through nozzle on tube section is less than V for example V the ejector functions as required and air from tube 13 is added to V until the maximum value V is flowing through the mixing chamber. However, if V is greater than V a certain volume of air is emitted into tube 13 until V equals V Under that condition, the diaphragm will be forced to a position other than that desired, and the resultant antenna pattern is distorted.

The regulator may be fixed to maintain the air pressure over a selected range of altitudes at a substantially constant value, such as, for example, at 12 p.s.i.g.; or it may be adjusted by changing the spring tension on a diaphragm for maintaining the pressures at different values. Regulators are well known in the art and, therefore, regulator 2 is not described in detail herein.

Referring now to FIG. 2 wherein is shown a graphical representation of the system transfer time (e.g., the time required for the diaphragm reflector to transfer from one surface of the antenna .to the other surface) versus altitudes for a family of gage pressures. It should be understood that the information in FIG. 2 is exemplary only and represents the transfer time for one embodiment of an ejector system. Various size ejectors known to those skilled in the art may change the shape of the curves somewhat. Primary pressure, P (see FIG. 1) is expressed in the graphical representation in terms of gage pressure, which is well known to be the difference between the absolute pressure of a confined fluid and the ambient or atmospheric pressure. For example, if the absolute pressure (expressed as p.s.i.a.) of a confined fluid at sea level is equal to 26.7 p.s.i.a., the gage pressure thereof would equal the absolute pressure minus the ambient pressure of 14.7 p.s.i. or 12 p.s.i.g. At 75,000

feet altitude, the absolute pressure becomes 12.5 p.s.i.a. which is the sum of the ambient pressure of 0.5 p.s.i. and the gage pressure of 12 p.s.i.g. Gage pressure is controlled by adjusting the regulator 2 (in FIG. 1) or by substituting one regulator for another. The values 5, l0, l2, l5 35 shown on the graph represent gage fluid pressure in p.s.i. from regulator 2. For the embodiment described, the fluid is air from a turbine engine regulated in regulator 2. In the graph, it can be seen that at the higher altitudes, transfer time increases and at each primary air pressure there is a corresponding altitude where choking Will occur. For example, with primary air pressure controlled at 12 p.s.i.g., the choking a1- titude is approximately 90,000 feet for the exemplary pneumatic design configuration illustrated.

*If a transfer time of 3 or less seconds is desired for an antenna diaphragm in an 8800 cc. change, for example, a gage pressure of approximately 12 p.s.i.g. is to be preferably maintained as indicated on the graph. For the exemplary design configuration illustrated, an ejector is preferably selected which has an air flow capability of at least 6.22 -cc./min. Therefore, the regulator is set to maintain P at 12 p.s.i.g. between 15,000 and 20,000 feet.

Referring again to FIG. 1., the operational cycle for the system is described. Air from the operating exemplary turbine engine (not shown) is directed into line 10 to regulator 2 which assumptively reduces the pressure to 12 p.s.i.g. The regulated pressure P also called the ejector primary pressure, passes through ejector 1 and exhausts into the atmosphere. As shown in the sectioned ejector, pressurized air exhausts from the tube 14 to the atmosphere through part 16 via chamber 17. Section 18 of valve 3 is set to provide fluid communication between parts 19 and 20. The air from tube 14 exhausts into nozzle 16 and draws air from chamber 17 into the atmosphere. As the air from chamber 17 is drawn out and exhausted, a region of reduced pressure is created at the juncture of line 13 in chamber 17 which results in the air being drawn from 1 3 and the chamber portion 25 of the antenna between diaphragm 6 and side 7. As the air is evacuated from the antenna chamber 25, the diaphragm is pulled against side 7, and a corresponding antenna pattern is mantained.

For the valve portions shown in FIG. 1, air from the atmosphere flows through line .1 2 and fills the chamber portion 26 of the antenna between diaphragm 6 and side 8 urging diaphragm 6 against side 7. The pressure of the air inside the chamber is the same as the pressure of the atmosphere; therefore, there is no Bourdon effect as occurs with positive pressure actuated devices. Depending on the factors discussed herein, the complete transfer may be completed in 3 seconds or less. Even though a transfer has been completed, the ejector continues to draw air from line 13; and in order to prevent rupture of the diaphragm, relief valve 9 may be incorporated into the system in line 13. Valve 9 is set to open at a line vacuum reflecting the normal vacuum oc curring after a transfer of the diaphragm is completed. For example, the vacuum in line 13 without a relief valve may vary from approximately 24 inches of mercury (Hg) at sea level to 4 inches of mercury at 40,000 feet. With a relief valve included and set to open at 6 inches of mercury, the 24 inches in Hg would never occur at sea level; at 40,000 feet the valve does not open.

A check valve 24 may also be added to prevent air from flowing into line 13 from tube 14 under choking conditions. Under choking conditions, instead of the air flowing from tube 14 and drawing air from line 13, the air flows into line 13 and moves the diaphragm from a selected surface area thereby interfering with an antenna pattern. If the condition continues, a detrimental Bourdon tube effect may also occur, thereby disturbing or varying the resultant antenna pattern. The check valve prevents the flow of air into the line and eliminates the harmfiul ballooning effects which could result.

If the position of valve 3 is switched to a second position, for example by energizing a solenoid, section 1 8 would provide fluid communication between parts 20 and 23, and section 2 1 provides fluid communication between parts 19 and 22. Air is then evacuated from the antenna chamber between diaphragm 6 and side 8, and the diaphragm is pulled against side 8 as discussed above in connection with side 7, whereby a second antenna pattern is provided. In other words, valve 3 may 'be positioned so as to selectively position diaphragm 6 in one of two alternative positions, thereby controlling the resultant antenna pattern.

If desired, a filter 31 may be added to prevent undesirable particles from flowing into the antenna chamber, case 5, from the atmosphere.

Line sizes are selected to cooperate with the ejector and regulator sizes. The selection of specific configurations the lines, regulator, ejector, relief valve, and other elements may be made for any desired set ofoperating conditions, employing ordinary skill.

Accordingly, there has been described improved antenna actuation means comprising an evacuating pneumatic control means for urging a deformable antenna reflector into one or two alternative positions. The pneumatic control means described avoids ballooning, and provides greatly improved response time. Further, the described arrangement employs no moving mechanical parts, whereby a small, lightweight unit having high-reliability, is provided.

Although the invention has been described and illustrated in detail, it is to be understood that the same is by way of illustration and example only, and is not to be taken by way of limitation; the spirit and scope of this invention being limited only by the terms of the appended claims.

-1 claim:

1. An antenna comprising:

first and second bulkheads defining a chamber case;

a deformable reflective diaphragm mounted in said case between said bulkheads to define a first and second chamber;

evacuating pneumatic control means for evacuating one of said chambers and venting the other to the atmosphere whereby said diaphragm is selectively urged against a selected one of said bulkheads.

2. A pneumatic control system for changing a radar beam pattern from broad to sharp and vice versa and adapted to be connected to a source of pressurized [fluid comprising:

antenna means comprising a hollow chamber case, said case containing a flexible metallic impregnated diaphragm transferable from one side of said case to the other side for changing a radar beam pattern from broad to sharp; regulator means ejector means connected to said regulator and said antenna for transferring said diaphragm from one side to the other;

said regulator means comprising means for controlling the pressure of said fluid so as to avoid choking of said ejector, said regulator means comprising safety valve means for providing an atmospheric intake to the ejector means at a predetermined pressure; and

selector means inserted between said ejector and said antenna comprising a two-way valve for selecting the shape of said radar beam pattern.

References Cited by the Examiner UNITED STATES PATENTS 1,158,690 11/1915 Jones 103-258 2,212,128 8/1940 Richter 343-915 2,977,596 3/1961 Justice 34-3-915 3,001,196 9/1961 HERMAN KARlL SAIALBACH, Primary Examiner.

A. R. MORGANSTERN, M. NUSSBAUM,

Assistant Examiners.

Mc llroy et a1. 343915 

1. AN ANTENNA COMPRISING: FIRST AND SECOND BULKHEADS DEFINING A CHAMBER CASE; A DEFORMABLE REFLECTIVE DIAPHRAGM MOUNTED IN SAID CASE BETWEEN SAID BULKHEADS TO DEFINE A FIRST AND SECOND CHAMBER; EVACUATING PNEUMATIC CONTROL MEANS FOR EVACUATING ONE OF SAID CHAMBERS AND VENTING THE OTHER TO THE AT 